InputText, ImDrawList: Fixed assert triggering when drawing single line of text with more than ~16 KB characters. (#3349)

docs/CHANGELOG.txt

@@ -37,6 +37,11 @@ HOW TO UPDATE?
 
 Other Changes:
 
+- InputText, ImDrawList: Fixed assert triggering when drawing single line of text with more
+  than ~16 KB characters. (Note that current code is going to show corrupted display if after
+  clipping, more than 16 KB characters are visible in the same low-level ImDrawList::RenderText
+  call. ImGui-level functions such as TextUnformatted() are not affected. This is quite rare
+  but it will be addressed later). (#3349)
 - ImDrawList: Thick anti-aliased strokes (> 1.0f) with integer thickness now use a texture-based
   path, reducing the amount of vertices/indices and CPU/GPU usage. (#3245) [@Shironekoben]
   - This change will facilitate the wider use of thick borders in future style changes.

docs/TODO.txt

@@ -308,7 +308,8 @@ It's mostly a bunch of personal notes, probably incomplete. Feel free to query i
  - font/atlas: dynamic font atlas to avoid baking huge ranges into bitmap and make scaling easier.
  - font/draw: vertical and/or rotated text renderer (#705) - vertical is easier clipping wise
  - font/draw: need to be able to specify wrap start position.
- - font/draw: better reserve policy for large horizontal block of text (shouldn't reserve for all clipped lines)
+ - font/draw: better reserve policy for large horizontal block of text (shouldn't reserve for all clipped lines). also see #3349.
+ - font/draw: fix for drawing 16k+ visible characters in same call.
  - font/draw: underline, squiggle line rendering helpers.
  - font: optimization: for monospace font (like the default one) we can trim IndexXAdvance as long as trailing value is == FallbackXAdvance (need to make sure TAB is still correct), would save on cache line.
  - font: add support for kerning, probably optional. A) perhaps default to (32..128)^2 matrix ~ 9K entries = 36KB, then hash for non-ascii?. B) or sparse lookup into per-char list?

imgui_draw.cpp

@@ -517,7 +517,7 @@ void ImDrawList::_OnChangedVtxOffset()
     // We don't need to compare curr_cmd->VtxOffset != _CmdHeader.VtxOffset because we know it'll be different at the time we call this.
     _VtxCurrentIdx = 0;
     ImDrawCmd* curr_cmd = &CmdBuffer.Data[CmdBuffer.Size - 1];
-    IM_ASSERT(curr_cmd->VtxOffset != _CmdHeader.VtxOffset);
+    //IM_ASSERT(curr_cmd->VtxOffset != _CmdHeader.VtxOffset); // See #3349
     if (curr_cmd->ElemCount != 0)
     {
         AddDrawCmd();
@@ -582,6 +582,9 @@ void ImDrawList::PrimReserve(int idx_count, int vtx_count)
     IM_ASSERT_PARANOID(idx_count >= 0 && vtx_count >= 0);
     if (sizeof(ImDrawIdx) == 2 && (_VtxCurrentIdx + vtx_count >= (1 << 16)) && (Flags & ImDrawListFlags_AllowVtxOffset))
     {
+        // FIXME: In theory we should be testing that vtx_count <64k here.
+        // In practice, RenderText() relies on reserving ahead for a worst case scenario so it is currently useful for us
+        // to not make that check until we rework the text functions to handle clipping and large horizontal lines better.
         _CmdHeader.VtxOffset = VtxBuffer.Size;
         _OnChangedVtxOffset();
     }